1. Technical Field
The present invention relates to a storage device, and more particularly to a security function.
2. Related Art
Since flash memory is compact, large-capacity, nonvolatile memory, a range of applications of the memory is rapidly widening. For example, the USB memory has increased in capacity and widely used as an auxiliary storage device of a computer. However, the security of the USB memory, or the like, cannot be said to be perfect, and important data in the memory may leak when lost or stolen.
JP 2006-59228 A describes a storage device intended for thoroughly erasing data, such as that fetched from a predetermined information processing apparatus and temporarily stored, at the time of occurrence of a specific event. Data captured from a personal computer by way of a USB terminal are stored in RAM serving as volatile memory. When a timer has detected elapse of a time selected by a user, refreshing operation of the RAM performed by a refresh circuit is stopped, to thus erase the data stored in the RAM and authentication data pertaining to the user used for encryption.
JP 11-175406 A also describes an auxiliary storage device intended for reliably preventing an unauthorized access such as to extract stored information by disintegrating information equipment. When unauthorized access is detected, a security processing section performs processing, such as erasure, encryption, or saving of data into another area.
However, a configuration for continually refreshing the entire volatile memory by means of a built-in battery affects an absolute time to retain data, and the absolute time becomes inversely proportional to the capacity of the flash memory. It may also be the case where a decrease in voltage of the built-in battery will pose a problem in refreshing operation before a time set in the timer by the user. Further, even when a malicious stranger has removed the USB memory from the personal computer without authorization during the course of use of the USB memory, the stranger may be afforded a sufficient time to extract data or disintegrate the memory until the time previously set in the timer.